using Application.Abstractions.Cache;
using Application.Abstractions.Data;
using Application.Abstractions.Messaging;
using Application.Abstractions.YouTube;
using Microsoft.EntityFrameworkCore;
using SharedKernel.Results;

namespace Application.Features.Api.Channel.GetCreators;

public sealed class Handler(
    IAppDbContext db,
    IYouTubeChannelCache channelCache,
    IYouTubeLiveStateStore liveStateStore,
    ICacheService cache
) : IQueryHandler<Query, Result<Response>>
{
    private const string CacheKey = "channel:creators:main";
    private static readonly TimeSpan CacheTtl = TimeSpan.FromSeconds(30);

    public async Task<Result<Response>> Handle(Query request, CancellationToken ct)
    {
        var cached = await cache.GetAsync<List<CreatorItem>>(CacheKey, ct);
        if (cached is not null)
        {
            return new Response(cached);
        }

        var items = await BuildAsync(ct);
        await cache.SetAsync(CacheKey, items, CacheTtl, ct);

        return new Response(items);
    }

    private async Task<List<CreatorItem>> BuildAsync(CancellationToken ct)
    {
        // 활성 채널 + 회원 집계(팔로워)·등급 조인. 구독자/썸네일은 아래 YouTube 캐시에서 보강.
        var rows = await db.Channel.AsNoTracking().Where(c => c.IsActive).Select(c => new
        {
            c.SID,
            c.Name,
            c.Handle,
            FollowerCount = c.Member.MemberStats != null ? c.Member.MemberStats.FollowerCount : 0,
            GradeName = c.Member.MemberGrade != null ? c.Member.MemberGrade.KorName : null,
            GradeImage = c.Member.MemberGrade != null ? c.Member.MemberGrade.Image : null,
            GradeColor = c.Member.MemberGrade != null ? c.Member.MemberGrade.TextColor : null
        }).ToListAsync(ct);

        if (rows.Count == 0)
        {
            return [];
        }

        // 구독자 수·썸네일은 Redis YouTube 캐시에서 (엔티티 컬럼은 30일 미동기 시 0/null 로 비워짐)
        var ytCache = await channelCache.GetManyAsync(rows.Select(r => r.SID));

        var allLive = await liveStateStore.GetAllLiveAsync();
        var liveMap = allLive.Where(l => l.IsLive).ToDictionary(l => l.ChannelId);

        var items = new List<CreatorItem>(rows.Count);
        foreach (var r in rows)
        {
            var hasYt = ytCache.TryGetValue(r.SID, out var yt);

            items.Add(new CreatorItem(
                r.SID,
                r.Name,
                r.Handle,
                hasYt ? yt!.ThumbnailUrl : null,
                hasYt ? yt!.SubscriberCount : 0,
                r.FollowerCount,
                r.GradeName,
                r.GradeImage,
                r.GradeColor,
                liveMap.ContainsKey(r.SID)
            ));
        }

        return items;
    }
}